Related art optical disk recording reproducers reproduce data recorded on optical disks such as compact disks (CD), digital versatile disks (DVD), etc. Related art reproducers do so by restoring radio frequency (RF) signals from the optical disks. For example, optical disk recording reproducers irradiate light onto optical disks, detect reflected light using photo diodes (PD), generate RF signals using the detected light, and slice generated RF signals into a constant level to restore data.
RF signals may have different amplitudes according to; for example, a difference in reflectivity between disks, a difference in reflectivity between inner and outer circumferences of disks, a change in inclinations of laser diodes, etc. To accurately restore data, RF signals must be sliced relatively accurately, and maintain a constant amplitude. Related art optical disk recording reproducers include automatic gain controllers for assisting in more accurately restoring data.
Automatic gain controllers feed back outputs of optical disk recording reproducers and control gain so that output signals maintain a constant amplitude. A related art redundant automatic gain controller will now be described with reference to FIG. 1.
FIG. 1 is a block diagram of a related art automatic gain controller 100. Referring to FIG. 1, RF signals detected by an optical pickup (not shown) are input to the automatic gain controller 100. The input RF signals are differential signals AGCIP and AGCIN having opposite phases and which have varying amplitudes.
The automatic gain controller 100 controls gain in response to a control voltage VCTRL. For example, the input RF signals AGCIP and AGCIN are amplified by a variable gain amplifier (VGA) 111, and an automatic gain control (AGC) output unit 113 produces output RF signals AGCOP and AGCON The automatic gain controller 100 may further include an equalizer EQ 115 and a slicer (not shown). The equalizer EQ 115 equalizes the output RF signals AGCOP and AGCON. The slicer slices the equalized output RF signals EQOP and EQON to a desired level. The sliced output RF signals AGCOP and AGCON are converted into digital signals, to restore data.
The gain of the automatic gain controller 110 is controlled in response to control voltage VCTRL as mentioned above. An example operation of controlling the control voltage VCTRL using the automatic gain controller 100 will be described below.
The control voltage VCTRL may be controlled by feeding back the output RF signals AGCOP and AGCON whose amplitude is controlled by the automatic gain controller 100 or by feeding back the equalized output RF signals EQOP and EQON. An example operation of controlling the control voltage VCTRL using equalized signal feedback will be described below.
The equalized output RF signals EQOP and EQON are filtered by a high pass filter (HPF) 121 and the filtered RF signals EQOP and EQON are output to a comparator 123 and a level detector 125. The comparator 123 compares the filtered RF signals EQOP and EQON and outputs a comparison signal CMP. The comparison signal CMP is used to control a response time of the automatic gain controller 100.
The level detector 125 detects peak and bottom levels of the filtered RF signals EQOP and EQON and outputs a voltage level signal LVLO. Each of the comparison signal CMP and the voltage level signal LVLO are output to a voltage controller 127. The voltage controller 127 detects a difference between the voltage level signal LVLO and a reference voltage and controls the control voltage VCTRL based on the difference.
For example, the voltage controller 127 may include a charge pump (not shown). The charge pump supplies charges to external capacitors CAGCID, CAGCUD or CAGROM according to the difference in voltage. The control voltage VCTRL is controlled based on voltages stored in the external capacitors CAGCID, CAGCUD or CAGROM. The automatic gain controller 100 uses the control voltage VCTRL to control the gain, and the MUX 131 selects one of the capacitors CAGCID, CAGCUD and CAGROM based on types of disk. For example, in case that RAM disk is used, MUX 131 selects capacitor CAGCID in response to RAM disk indication signal RAM and header signal HD. The external capacitors CAGCID, CAGCUD and CAGROM may be classified into types of disks. Charges supplied from the charge pump are stored in different external capacitors CAGCID, CAGCUD or CAGROM according to the type of disk.
The voltage controller 127 controls a current input to the charge pump in response to the comparison signal CMP, thereby controlling a setting time of the automatic gain controller 100. When a fingerprint and/or scratch exists on the disk of the voltage controller 127, a hold signal HOLD may hold or temporarily stop controlling an automatic gain in response to header signal HD and control signal VFO determined in response to the types of disks. When data is recorded on disks, the fixed voltage generator 129 outputs a fixed voltage using a fixed gain signal FIXG, and the voltage controller 127 outputs the fix signal. The fixed voltage may be transmitted in response to the fix signal FIX.
However, because the automatic gain controller 100 has a complex analogue control circuit for generating the control voltage VCTRL, it may be more difficult to implement the automatic gain controller 100 on a system on chip (SOC).
For example, the automatic gain controller 100 requires a separate block for controlling a response time according to a disk speed and separate external capacitors CAGCID, CAGCUD, and CAGROM for storing charges supplied from the charge pump. This increases the required number of pins corresponding to the external capacitors CAGCID, CAGCUD and CAGROM.
The automatic gain controller 100 further includes a separate reference voltage generator comprising a digital-analogue converter for generating a reference voltage and a separate fixed voltage generator 129 for acquiring a fixed gain.
The automatic gain controller 100 also requires many control signals for controlling an analogue circuit resulting in a more complex circuit layout and the charge pump and capacitors have a fixed capacitance, which slows a response in emergency. In addition, characteristic distribution between devices is relatively wide.